1. Field of the Invention
The present invention relates to a detecting device for detecting the position of an electronic component in which the component is held by a holder, by irradiating the electronic component so as to produce a projection image of the component. More particularly, the present invention is concerned with improvements of the detecting device for simple and accurate detection.
2. Discussion of the Prior Art
The above type of detecting device is known in the art. An example of such a detecting device is disclosed in laid-open Publication No. 60-28298 of unexamined Japanese patent application, in which a light emitter projects light toward a reflecting plate so that the light is reflected by the reflecting plate toward the electronic component, and then received by a charge-coupled device to provide a projection image of the electronic component. In this type of device, the reflecting plate and the charge-coupled device are disposed on the opposite sides of the electronic component, while the light emitter is disposed on the same side as the charge-coupled device to project light toward the reflecting plate. In this arrangement, if the light emitted by the light emitter is directly incident upon and reflected by the electronic component, the reflected light is received by the charge-coupled device, causing adverse influence on the projection image of the electronic component, which results in reduced detecting accuracy of the device. For avoiding this inconvenience, the electronic component is provided with a shielding plate so as to prevent the light emitted by the light emitter from impinging directly on the component.
However, if the electronic component to be held by the device is changed in size, the shielding plate for shielding the electronic component must be replaced by another, in accordance with the size of the component. In this respect, it is to be noted that when the electronic component is exposed to the light reflected by the reflecting plate to provide the projection image thereof, the shielding plate is required to prevent direct exposure of the electronic component to the light emitted from the light emitter, and also to allow the light to impinge on a portion of the reflecting plate which is sufficiently close to the component holder, so that the reflecting plate can reflect the light at that portion which lies within the outline of the electronic component, as well as the surrounding portion outside the periphery of the component. This requirement increases as the size of the electronic component becomes smaller. When the shielding plate appropriate for relatively large electronic components is used for shielding a relatively small component, only the outer portion of the reflecting plate remote from the component holder is irradiated by the light from the light emitter, resulting in an insufficient amount of light reflected by the reflecting plate. On the other hand, when the shielding plate appropriate for relatively small electronic components is used for shielding a relatively large component, the shielding plate cannot sufficiently prevent direct exposure of the electronic component to the light emitted from the light emitter. For these reasons, it is necessary to provide a shielding plate which is suited for each size of the electronic component, resulting in an increased cost of the detecting device, which may require many kinds of shielding plates. Further, a cumbersome procedure is necessary to change the shielding plate each time the size of the electronic component is changed.